Multi-layered structures and materials are commonly used in many industries, such as the automotive and building industries. One common use for multi-layer structures is for automobile headliners, panels and dashboards where multiple layers of thermoplastic and/or other materials are shaped, laminated together and formed into a structure having the desired physical and aesthetic or decorative properties. For example, a cover layer such as cloth, having the desired decorative surface (e.g. texture, grain, color and the like) may be laminated to a substrate having desirable physical characteristics (e.g. shape, strength, rigidity, hardness, softness, surface quality and the like). One or more additional layers may be added to vary the physical and decorative characteristics.
Existing methods for producing such molded, multi-layer structures are inefficient, expensive and limited in the variations of the molded product that can be produced. According to one such existing method, the multiple layers are combined and laminated simultaneously during the thermoforming of the molded, multi-layer structures.
One such method includes injection molding a substrate and applying an adhesive, such as a spray adhesive or adhesive film, to the substrate. The substrate is placed in or on a thermoforming mold, and a heated thermoplastic layer is stretched and vacuum drawn over the substrate, while the substrate is in the mold, until bonded to the substrate. Other methods include adding one or more additional layers between the substrate and cover layer while in the mold and require even more complex equipment and steps of forming and shaping the cover layer so that the additional layers can be applied between the substrate and cover layer.
One significant disadvantage of these existing methods is the complexity of the process. Having to perform the lamination of the multiple layers together and simultaneously with the thermoforming requires complex and expensive machinery, additional chemicals and materials, additional manufacturing time, and close attention to molding temperatures and time so as not to damage the materials being laminated.
Another limitation with existing methods of forming molded, multi-layer structures is in the variations of the product that can be produced. To vary the thickness or rigidity of the multi-layer structure, for example, requires additional layers of material having varying properties and placement of these layers in precise locations with respect to other layers in the mold to accomplish the desired thickness or rigidity of the molded, multi-layer structure. Forming a textured or decorative surface on the cover layer also typically requires additional manufacturing steps and equipment, further increasing manufacturing costs and time. Moreover, the finished product often includes layers of dissimilar materials, adhesives and other additives, resulting in a molded product that is difficult or impossible to recycle.
The complex and inefficient existing methods of laminating simultaneously with the thermoforming process were previously necessary to produce a molded product with the desired shape and appearance. Attempts at pre-laminating the layers prior to thermoforming the multi-layer structure have been unsuccessful because the heating of the pre-laminated structure during thermoforming was ineffective and destructive to the molded product. The heating used in existing thermoforming methods would scorch or burn the outer surfaces of the substrate layers without adequately heating the center of the substrate layer to allow forming of the product. Any textured or decorative surface of the cover layer applied to the substrate would then be damaged during the thermoforming process.
Accordingly, a need exists for a method of forming a molded, multi-layer structure in which a pre-laminated, multi-layer structure having a thermoplastic substrate layer and a cover layer can be used in a thermoforming process to efficiently and quickly, in one step, form a molded, multi-layer structure having any desired shape, thickness, rigidity, texture, appearance, or any other desired physical or decorative characteristic. A method is needed in which a textured or decorative surface can be applied on a cover layer of the multi-layer structure either prior to forming or during the thermoforming process without being damaged by heat during the thermoforming process. A method is also needed in which the thickness and/or hardness/softness of the multi-layer structure can be varied during the thermoforming step. A method is also needed for forming a molded, multi-layer structure that is easily and fully recyclable.